Adaptive power control for orthogonal signal-division multiplexing underwater acoustic communications

As a generalized framework unifying the traditional orthogonal frequency-division multiplexing (OFDM) and single-carrier frequency-domain equalization (SC-FDE), orthogonal signal-division multiplexing (OSDM) has emerged as a promising modulation scheme for building reliable underwater acoustic communication (UAC) systems. However, given the temporal and spatial variability of acoustic links, the received changing signal strength can pose a serious performance-degrading factor for the actual OSDM systems. This paper resorts to the feedback-based adaptive power control (APC) and builds smart OSDM systems that can maintain the signal-to-noise ratio (SNR) of the received signal at a pre-specified level, thus affording substantial gains in either power savings or link quality improvement. We first introduce the underwater OSDM system and formulate its APC procedure. Then, an innovative solution for establishing an initial link with a more efficient initial power instead of the traditionally used maximum power of the transmitting transducer is presented. Next, we focus on the APC techniques and propose three different algorithms in both the fixed-step and variable-step categories. Finally, simulation results are presented to demonstrate the feasibility and effectiveness of the proposed OSDM-APC system.